Characterization of aqueous carbonated cement-based materials by multinuclear solid-state NMR spectroscopy

Solid-state nuclear magnetic resonance (NMR) spectroscopy is a versatile characterization technique to investigate complex systems such as cement-based materials. This work summarizes recent advances in the application of solid-state NMR spectroscopy for analyzing carbonation processes of cement-based materials on an atomistic level. ²⁹Si MAS NMR can probe the progressive decalcification and subsequent decomposition of the C-(A)-S-H phase as well as the formation of the alumina-silica gel. Detailed structural information about the alumina-silica gel can be achieved from ²⁷Al and ²⁹Si NMR, where the present work focusses particularly on the early-stage structure of this phase, exhibiting a higher Al/Si ratio and hydroxylated AlO₄ sites. It is also shown that a quantification of carbonate phases can be obtained by ¹³C MAS NMR, whereas ¹³C{¹H} cross-polarization (CP) NMR measurements allow identification of hydrous carbonate sites. Insights about the reactivity and thermal stability of the carbonation products are also provided by ²⁹Si and ²⁷Al MAS NMR.